The typical wastewater treatment plant includes a final clarifier in which the suspended solids from the prior treatment step is allowed to settle out. These solids generally have very low settling rates which makes the hydraulic efficiency of the tank quite important. Until about 1958, a final clarifier was invariably of the center feed type; since then the advantages of peripheral feed as disclosed in U.S. Pat. Nos. 2,961,099 and 2,961,100 have been demonstrated.
In such tanks, the peripheral feed channel or channels are of diminishing cross-section and can be provided with a series of relatively large ports which are relatively free of clogging. Generally, all of such ports may be of the same size and spaced to provide the equal distribution of the feed around the tank. Where especially large ports are provided, a lower distribution baffle as in U.S. Pat. No. 3,228,530 may also be provided.
In recent years the waste in some treatment plants has included grease solids which are not always entirely removed by the prior treatment step; this has made it necessary to provide for skimming of the tank and the peripheral feed channel.
U.S. Pat. No. 3,136,724 shows manually operable gates for the selective removal and disposal of the scum which has collected at the ends of the peripheral feed channels. The object of the present invention is to provide dependable and readily adjustable means for removing the accumulated scum from the feed channel but which does not require manual attention or an automatic timing and operating mechanism. The invention is based upon the regular, daily variation in the flow through the usual sewage treatment plant and the observation that as the flow increases, somewhat more grease passes through the plant untreated and the accumulation continues to about the time the flow rate diminishes towards its low day- or night-time rate.